This invention relates to a method of multistage continuous fermentation.
Continuous fermentation of microorganisms involves the continual removal of broth and microorganisms from a fermentor coupled with the addition of fresh medium so that no change in volume, or other relevant parameters, occurs. The rate of removal and addition determines the rate at which the microorganisms may grow. Similarly, the medium and environmental conditions will determine the biochemical pathways which the microorganisms utilize, and therefore the end products of the fermentation.
Lindblom et al. U.S. Pat. No. 3,328,262, discloses apparatus having two continuous fermentation vessels comprising (a) a growth vessel for Xanthomonas with minimal product formation and (b) a production vessel for polysaccharide production. The vessels are controlled so that pH, temperature, oxygen and mean cell residence time are optimal for growth or product production, respectively.
Heady et al. U.S. Pat. No. 4,520,104 discloses the production of butanol by a continuous fermentation process using Clostridium acetobutylicum. The process involves the use of a continuous culture vessel containing cells in a logarithmic phase of growth, which provides a continuous inoculum for a second fermentation vessel. The butanol produced by these cells is detrimental to their growth and thus conditions in the first fermentor are maintained such that the level of butanol is minimal. Butanol formed in the second fermentation vessel is removed continuously using a filter system, and the cells are periodically recycled.
Weisrok et al. U.S. Pat. No. 4,418,145 discloses the production of Xanthomonas campestrius and a process for its use to produce xanthan from a nutrient medium. Either one or two fermentors may be used. If two fermentors are used, the first provides logarithmically growing cells to the second fermentation unit which contains a nutrient medium similar to that of the first unit but with more glucose to induce product formation. Xanthan is continually removed from the effluent of the second fermentor.